Abstract

Aminoglycoside antibiotics are used to treat life-threatening bacterial infections but can cause deafness due to hair cell death in the inner ear. Compounds have been described that protect zebrafish lateral line hair cells from aminoglycosides, but few are effective in the cochlea. As the aminoglycosides interact with several ion channels, including the mechanoelectrical transducer (MET) channels by which they can enter hair cells, we screened 160 ion-channel modulators, seeking compounds that protect cochlear outer hair cells (OHCs) from aminoglycoside-induced death in vitro. Using zebrafish, 72 compounds were identified that either reduced loading of the MET-channel blocker FM 1-43FX, decreased Texas red–conjugated neomycin labeling, or reduced neomycin-induced hair cell death. After testing these 72 compounds, and 6 structurally similar compounds that failed in zebrafish, 13 were found that protected against gentamicin-induced death of OHCs in mouse cochlear cultures, 6 of which are permeant blockers of the hair cell MET channel. None of these compounds abrogated aminoglycoside antibacterial efficacy. By selecting those without adverse effects at high concentrations, 5 emerged as leads for developing pharmaceutical otoprotectants to alleviate an increasing clinical problem.

Figure 1

(A) Cranial and trunk neuromasts in a control larva treated with FM 1-43FX and imaged with the Phenosight system, (B) a larva in which the compound blocked FM 1-43FX entry into hair cells, and (C) a larva that became fluorescent in which neuromasts could not be screened. (D–F) Scatter plots showing all results for each screen. Compounds are grouped according to biological activity. Compounds were given a score where 0 = toxic, 1 = no block or no protection, 2 = weak block or partial protection, and 3 = full protection. Each screen was repeated 3 times so the pass threshold is >3 (at least 1 screen with a score higher than 1), fail = 3 (3 screens each with a score of 1), and toxic < 3. Colored dots identify compounds that protected hair cells in mouse cochlear cultures from gentamicin: green dots identify those that blocked the MET channel, and red dots identify those that did not block the MET channel. All larvae were at 4 dpf. Scale bar: 1 mm.